A potential cause of head injuries in vehicle rollover accidents occurs when a vehicle roof impacts the ground. The impact may cause the roof to deform and to impact an occupant's head. A headliner may not provide enough cushioning to mitigate head trauma and injuries in such a rollover accident. Deploying an airbag above the head of a vehicle occupant could mitigate this potential head trauma. However, existing mechanisms for over-the-head airbags suffer from various deficiencies. For example, an airbag deployed from a vehicle seat back may undesirably force the occupant's head forward, and/or cause neck discomfort. Further, mechanisms to deploy over-the-head airbags from seat headrests require costly and aesthetically displeasing components to activate the airbag. Accordingly, there is a need for an improved over-the-head (or roof) airbag system.